atom retina fix - I am using Spacegray Dark Theme but the code should be a starting point for other themes as well

styles.less

atom-text-editor {
  font-size: 24px;
}

.tab-bar {
  height: 60px;
  .tab {
    padding-right: 48px;
    max-width: 350px;
    min-width: 80px;
    height: 60px;
    line-height: 60px;
    font-size: 22px;
    &.active, &.active:before {
      height: 60px;
      line-height: 60px;
    }
    .close-icon::before {
      font-size: 24px;
      line-height: 60px;
      width: 24px;
      height: 24px;
    }
  }
}

.tab-bar .tab.modified:not(:hover) .close-icon {
  width: 16px;
  height: 16px;
  top: 22px;
  right: 22px;
}

.tree-view {
  font-size: 22px;
}

.list-group .selected::before, .list-tree .selected::before {
  height: 52px;
}

.list-group li:not(.list-nested-item), .list-tree li:not(.list-nested-item), .list-group li.list-nested-item > .list-item, .list-tree li.list-nested-item > .list-item {
  line-height: 52px;
}

html {
  font-size: 22px;
}

atom-text-editor[mini] {
  font-size: 22px;
}

.btn {
  font-size: 22px;
}

.find-and-replace .input-block-item, .project-find .input-block-item {
  padding: 10px;
}
.overlay, atom-panel.modal {
  width: 800px;
}

.list-tree.has-collapsable-children .list-nested-item > .list-item::before,
.list-tree.has-collapsable-children .list-nested-item.collapsed > .list-item::before {
  font-size: 24px;
  width: 24px;
  height: 24px;
}

.settings-view .section-container {
  max-width: none;
}

.config-menu {
  width: 360px !important;
}

linter-message, status-bar {
  font-size: 22px;
  height: 44px;
  line-height: 44px;
}

.key-binding {
  font-size: 20px;
}